The invention relates to a medical apparatus for reducing intraocular pressure by acting upon the Schlemm's canal and the tissue of the trabecular network directly in contact with the Schlemm's canal, comprising a probe with a photoconductor connectable to a laser.
International Patent Application No. WO 92/17138 A2 discloses a medical apparatus of this type having a laser, to which a probe is connected by a photoconductor. The end of the photoconductor or fiber optic is disposed in a sleeve which is introduced into the probe housing, and inside the housing there are additional light conducting means such as lenses and prisms for adjusting and deflecting the beams. The apparatus and especially the probe are not easy to use in microsurgery due to their large size.
Moreover, a method and an apparatus for microsurgery on the eye by laser radiation are disclosed in published German Patent Application No. DE-OS 38 31 141. This apparatus includes a handpiece in which a fiber optic or photoconductor, on the one hand, and on the other an aspirating or flushing system for removing the tissue ablated by the laser beam, are provided. The light issues frontally from the free end of the photoconductor, the end of the photoconductor being disposed together with the aspirating or rinsing system in a special head piece. This apparatus too has appreciable dimensions which limit its use in microsurgery to special cases.
Glaucoma is one of the most frequent causes of blindness in the industrial countries. The common characteristic of this class of diseases in by far the greatest number of cases is an elevation of the intraocular pressure above a level tolerated by the optical nerve and nerve sheath. Untreated, a progressive atrophy of the optical nerve takes place. The progressive loss of nerve fibers results in the late stages of the disease in advancing losses of peripheral vision, and if untreated an irreversible, complete loss of function occurs, plus blindness. Treatment is based on the particular form of the glaucoma, the lowering of the intraocular pressure being the most prominent. The cause of the pressure increase is an elevated resistance in the aqueous humor drainage system. More than 80% of the aqueous humor, which is formed at a rate of approximately 2.5 .mu.l/min, leaves the eye in the area of the corner of the anterior chamber, and more than 20% in the area of the ciliary body. Through the trabecular meshwork in the corner region of the chamber it reaches the Schlemm's canal and is carried through the aqueous humor veins under the conjunctiva, where resorption takes place in the vessels of the conjunctiva. The main resistance to drainage of the aqueous humor is in the inner wall of the Schlemm's canal and the adjacent trabecular meshwork. The treatment of glaucoma in the early stage of the disease is primarily with drugs. If sufficient pressure-reducing effect cannot be achieved, then surgical or laser surgery methods are employed. The methods heretofore available for intraocular pressure reduction other than by drug treatment are characterized by the fact that they do not act primarily at the locus of the most severe elevation of resistance.
Argon laser trabecular surgery is known, in which laser pulses are aimed through the anterior chamber at the trabecular meshwork via a contact glass with special lens systems on the slit lamp, which are intended to produce a stretching of the trabecular meshwork, and thus to improve the aqueous humor drainage into the Schlemm's canal. This procedure does result in a temporary reduction of intraocular pressure in most cases; however, due to the deflection of the laser beam by the anterior chamber onto the opposite side of the meshwork, the accuracy of aim is limited; the formation of adhesions (synechiae) in the area of the corner region of the chamber is one of the complications. In particular, it is difficult to control the depth of penetration of the laser pulses.
Also known is photoablation of the trabecular meshwork ab interno, in which either an erbium-Yag laser (Er:Yag) or a neodymium-Yag laser (Nd:Yag) or an excimer laser is used, whose pulses are aimed by means of fiber optics through the anterior chamber of the eye at the trabecular meshwork. Moreover, experiments have been undertaken to apply the laser pulses of an Nd:Yag laser through a contact glass at the opposite chamber corner region, without opening the eye. Alternately, ab interno sclerostomies also have been performed experimentally with pulsed dye lasers or argon lasers through a contact glass. Also in these methods it is difficult to control the depth of penetration of the laser pulses. Many experimenters are attempting a breakthrough effect through the adjacent sclera in order to open the subjunctival chamber (region directly under the pupil conjunctiva) and facilitate direct drainage in this region. Due to the scarring reactions these techniques have been unable to achieve any progress beyond a series of clinical experiments.
In the case of the known laser sclerostomy ab externo, a fistula for aqueous humor drainage under the conjunctiva has been created, in which after the ocular conjunctiva has been opened, the entire thickness of the sclera is penetrated. In this process an extensive defect is produced in the sclera. Any lasting resorption of the intraocular fluid requires that the access must not scar, but in this process it is a typical complication, the same as in the conventional operations performed manually. In contrast to the conventional surgical methods, however, the iris is not also partially removed (iridectomy) during laser sclerostomy, so that another possibility of complication is that the fistula may be closed by pulling in the iris. Attempts are often made to control the scarring from overshooting in the area of the conjunctiva through supplemental medication by antimetabolites, such as Mitomycin C or 5-fluorouracil. A serious disadvantage here is the toxicity of the substances used.
All of the experimentally tested medical devices and methods that are presently in clinical use have in common that they do not selectively achieve an improvement of the intraocular fluid drainage at the intraocular structures which are the locus of the main resistance in the system of drainage from the anterior chamber of the eye. In the known methods the laser pulse is aimed through the anterior chamber at the opposite tissue areas. In the known methods the first effects take place in the area of the trabecular meshwork, and the effects that likewise occur in the deeper structures cannot be evaluated.